Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 60)

60 Publication 1756-UM0009C-EN-P - December 2010
Chapter 4 Non-isolated Analog Voltage/Current Input Modules (1756-IF16, 1756-IF8)
Module Filter
The module filter is a built-in feature of the analog-to-digital convertor that
attenuates the input signal beginning at the specified frequency. This feature is
applied on a module-wide basis.
The module attenuates the selected frequency by approximately -3dB or 0.707
of the applied amplitude. This selected frequency is also called the bandwidth
of the module.
An input signal with frequencies above the selected frequency will be
attenuated more, while frequencies below the selection will receive no
attenuation.
In addition to frequency rejection, a by-product of the filter selection is the
minimum sample rate (RTS) that is available. For example, in floating point
mode, the 1000 Hz selection will not attenuate any frequencies less than
1000 Hz, but will allow sampling of all 16 channels within 18 ms. But the
10 Hz selection attenuates all frequencies above 10 Hz and allows only
sampling of all 16 channels within 488 ms.
Use the following table to choose a module filter setting.
IMPORTANT
The default setting for the module filter is 60 Hz. This setting
provides approximately 3 dB of filtering of a 60 Hz input.
Filter Selections with Associated Performance Data
Module Filter Setting
(-3dB)
(1) (2)
Wiring Mode 10 Hz 50…60 Hz
(Default)
100 Hz 250 Hz 1000 Hz
Minimum sample time (RTS)
Integer mode
Single-ended
Differential
High-speed differential
488 ms
244 ms
122 ms
88 ms
44 ms
22 ms
56 ms
28 ms
14 ms
28 ms
14 ms
7 ms
16 ms
8 ms
5 ms
Minimum sample time (RTS)
Floating point mode
Single-ended
Differential
High-speed differential
488 ms
244 ms
122 ms
88 ms
44 ms
22 ms
56 ms
28 ms
14 ms
28 ms
14 ms
7 ms
18 ms
11 ms
6 ms
Effective resolution 16 bits 16 bits 16 bits 14 bits 12 bits
(1) For optimal 50…60 Hz noise rejection (>80dB), choose the 10 Hz filter.
(2) Worst case setting time to 100% of a step change is double the RTS sample times.